Derbyshire has moved.  Not so much that you’d notice, but it has shifted.  The last big earthquake to hit the area happened on 12^th February 1957 and measured 4.2 on the Richter scale.  What may be more shocking about this is that a bigger tremor, measuring 5.3, hit the previous day at a quarter to four in the evening.  The epicentre was located just the other side of the county border at Castle Donnington.

          It might come as a surprise in itself, but earthquakes are not uncommon in Britain.  Only rarely though are they big enough for us to feel, like Derbyshire’s two tremors in 1957.  British buildings are quite robust, although some damage was reported in the Derby and Loughborough areas afterwards.  A falling chimney is also recorded as wounding a child in Derby, which demonstrates that our quakes can still be dangerous.

It is the British Geological Survey who records all the tremors that take place under our feet and in an average year they can register anything between 200 and 300 quakes.  That’s almost one every 36 hours!

          The Richter scale of measuring the amount of energy released during an earthquake was devised by C F Richter in America.  It was created in 1935 and is a logarithmic scale from 0 to 9, with 9 being the highest and most severe.  It is calculated using information from seismic recordings which measure the amount of energy released by the earth’s movements during a tremor.  It is wrong to assume that a quake measuring 6 is twice as powerful as one measuring 3 on the scale.  Each point on the Richter scale is actually 30 times more powerful than the previous point. Therefore a quake measuring 4 is 30 times more powerful than a quake measuring 3, and a quake measuring 5 is 900 times more powerful than a quake measuring 3 (30 x 30).

Earthquakes can occur anywhere in the world, although the majority take place where two of the earth’s crustal plates meet.  These plates are classified as “destructive” if they are pushing against each other, “constructive” if they are moving away from each other and “conservative” where they slide against each other.  One of the most famous of these conservative faults is the San Andreas Fault which stretches for over 800 miles through California in America.

          Britain does not lie along any of these major faults, which is why we don’t experience the violently large quakes that affect some areas of the world such as Japan, the Middle East and South America.  The nearest large fault is the mid Atlantic Ridge, which as its name suggests is in the middle of the Atlantic Ocean.  However, quakes can happen anywhere within in these huge plates and not just where they meet one another.  Britain sits on the Eurasian plate which is under constant pressure from two areas.  The Atlantic plate is moving away from the Eurasian plate, whereas the African plate is pushing it northwards.

          In the East Midlands there is an area of harder rock, referred to as the Midland Microcraton, and it is believed that this is affected by the surrounding softer rock being pressurised by the widening of the Atlantic plate.  This puts particular pressure on an area between Derby, Melton Mowbray and Peterborough.  Melton Mowbray was the epicentre of a quake registering 4.1 on 28^th October 2001.

          Quakes are more common in Britain the further west you are.  The largest quakes at the end of the 20th century took place in Bishop’s Castle on the Welsh Borders, the Llyn Peninsula in Wales and Carlisle.  However the largest quake to affect the whole of the British Isles actually took place in the North Sea in 1931 in an area known as Dogger Bank.  This lies approximately 75 miles off the coast of Great Yarmouth, and the quake measured 6.1.  It was felt across the Netherlands, Belgium, north France, Denmark as well as areas of Germany and Norway.  The shock waves rippled through large areas of Britain and Ireland.  Damage was reported across the country in over 70 places, including a church spire in Filey, which rotated.  A collapsed factory roof in Staines was also attributed to the quake.  Large waves battered the East Coast of Britain, but because the epicentre was out at sea, damage on land was far less than it could have been.

          Before 1957, the previous biggest quake to hit Derbyshire happened on 24^th March 1903 at half past one in the afternoon with a force equivalent to 4.6 on the Richter scale.  Since 1900, there have been 25 earthquakes shaking Britain with a magnitude of 4.5 or higher.  On average, a quake of 5 or more rocks our foundations every ten years.   Chesterfield shuddered on 10^th February 1997 to a minor 2.9 quake.

          As a result, properties are built to higher standards today which helps explain why damage is thankfully quite limited.  In 1884 though, an earthquake hit Colchester in Essex with a force equivalent to 4.6 on the Richter scale and created immense damage with church spires and chimneys falling through roofs.            Whilst damage to buildings is fairly minor, British earthquakes have been known to kill.  Since 1580, eleven people have died, including 6 by falling debris, 1 who fell out of a window, and another who committed suicide.  The last time someone died in Britain during a quake was on 12^th December 1940 in Criccieth, North Wales, when they fell down the stairs during the tremor.

          So next time you feel your knees tremble, don’t look into your pint glass and wonder whether now’s the time to stop drinking.  It could just be Mother Nature flexing her muscles.  Grab the nearest banister to make sure that you don’t fall down the stairs or take cover from falling debris and it could all be over in a matter of seconds.  The chances are though, you probably won’t even know anything has happened. 

 THE END